A major shift in Daphnia genetic structure after the first ice‐free winter in a German reservoir

Abstract

Summary 1. Climate warming may cause disruption of trophic linkages in aquatic ecosystems and lead to changes in abundance and genetic structure of zooplankton populations. We monitored the community of the Daphnia galeata‐hyalina hybrid complex in the Saidenbach Reservoir (Saxony, Germany) using allozyme electrophoresis for three consecutive years (2005–07), including one (2007) following an unusually warm winter that prevented the formation of ice cover for the first time in the history of the reservoir. 2. Genetic composition during the 2007 season differed substantially from the two preceding years that experienced the usual 3‐month ice period. Three abundance peaks in June, July and October 2007 were dominated by hybrids of Daphnia galeata x hyalina, whereas in the 2005 and 2006 seasons two peaks in June and September were dominated by Daphnia hyalina genotypes. 3. The genetic composition of the pool of diapausing eggs produced in autumn and the rate of change of genotype abundance during the following spring indicate recruitment of the D. hyalina subpopulation from ex‐ephippial animals during the spring population increase. 4. The differing potential to contribute to the overwintering animal pool or to the inoculum from diapausing eggs was confirmed by results from laboratory life‐table experiments. Daphnia galeata clones survived longer and produced parthenogenetic offspring under winter conditions, whereas D. hyalina clones showed a shorter lifespan and produced resting eggs. 5. Our results indicate a profound role of recruitment strategy in the observed shift in genetic composition. Increasing winter temperatures predicted in the context of climate change may thus favour overwintering animals, leading to an increase in the contribution of these genotypes to the population. Such microevolutionary processes may dampen possible seasonal mismatches between daphnid populations and their food or predator populations.

Strong differences in the clonal variation of two Daphnia species from mountain lakes affected by overwintering strategy

“…The contribution of individuals surviving the winter period to the next season's population may substantially differ, both among different localities (as observed by us) and among years within the same locality [19]. The overwintering clones may belong to the most successful ones within the population.…”

The response of temperate aquatic ecosystems to global warming: novel insights from a multidisciplinary project

“…In cold-winter years, genetic diversity of Daphnia increased significantly during spring, presumably due to a higher contribution of emergence from resting eggs to population growth (Hülsmann et al 2012). In addition, the genetic composition of the population differed substantially between cold-and warm winter years (Zeis et al 2010). This will affect physiological capabilities of the spring population to cope with high temperature and/or low oxygen (Pinkhaus et al 2007;Paul et al 2012), life history strategies, and potentially also the inducibility of defense strategies against predators (Hülsmann and Wagner 2007).…”

The effects of global warming on Daphnia spp. population dynamics: a review

“…These field observations were confirmed by laboratory experiments, where observed reaction norms mirrored life-history trait values from natural populations (Bernot et al 2006). Zeis et al (2010) showed that temperature regime changes may result in a shift in the balance between D. galeata and D. hyalina in their hybrid complex community (populations contain parental as well as hybrid genotypes). Daphnia galeata and D. hyalina genotypes are characterised by different potentials for resting egg production and different timings of ephippia formation and hatching events.…”

“…These authors observed that overwintering D. galeata clones appeared after an unusually warm winter in 2007, whereas all of the other years investigated, which had cold winters, were dominated by D. hyalina genotypes, which hatched from resting eggs. Zeis et al (2010) concluded that the increasing temperatures predicted under the context of climate change may favour overwintering animals, leading to an increase in the contribution of these genotypes to the population. The authors did not consider consequences of such phenomena for the genetic diversity of this community, although it might be expected that overwintering populations will be genetically less diverse than formed by hatchlings (e.g.…”